The correction of remote sensing radiometry for ocean color applications requires a highly accurate characterization of the optical instrument performance. For example, the Visible Infrared Imager Radiometer Suite (“VIIRS”) launched successfully on 28 Oct. 2011 employs a filter radiometer to remotely sense the atmosphere in 22 visible and infrared bands located in the 0.4-12.5 μm range. Products of VIIRS data are a crucial continuation for climate change study under NASA and support NOAA and DOD operational objectives.
The primary issues of VIIRS instrument are out-of-band (“OOB”) response and optical crosstalk. The OOB response is defined as the ratio of integrated response outside the one percent of peak response points of a spectral band to the integrated response for the band. The OOB effect produces a radiometric bias that depends on the source of radiance being measured and it could adversely impact VIIRS product quality. In ocean color applications, accurate and consistent sensor calibration is essential. Several multispectral radiometric instruments such as SeaWiFS and VIIRS are known to exhibit significant radiance contribution from OOB spectral response.
To deal with the Sea-viewing Wide Field-of-view Sensor (“SeaWiFS”) OOB effects, a methodology was developed for SeaWiFS calibration. Based on this methodology, an improved correction method to remove the spectral band effects of the SeaWiFS on the derived normalized water-leaving radiance which results in improved ocean near surface chlorophyll concentration is developed and implemented in the operational SeaWiFS data processing system. These calibration methods adjust the measured radiances to correct OOB response for ease of comparison to in situ measured multispectral radiances. The SeaWiFS correction scheme has been successfully applied to data products retrieved over case 1 ocean waters. However, the correction scheme is inherently not usable for SeaWiFS data product corrections over case 2 turbid waters or over land.
An alternative solution for recovering the in-band multispectral radiances for SeaWiFS and VIIRS instruments is developed by Chen and Gao (Chen, W., and B.-C. Gao, “A Multispectral Decomposition Technique for the Recovery of True SeaWiFS Top-of-Atmosphere Radiances”, IEEE Geosci. Rem. Sens. Lett., Vol 10, No 2, 10.1109/LGRS.2012.2203293, 2013, incorporated herein by reference), and Gao and Chen (Gao, B.-C., Wei Chen, “Multispectral decomposition for the removal of out-of-band effects of visible/infrared imaging radiometer suite visible and near-infrared bands”, Applied Optics, Vol. 51, Issue 18, pp. 4078-4086, 2012, incorporated herein by reference) using the Multispectral Decomposition Transform (“MDT”) method, respectively. The OOB correction by the MDT method is based on the characteristics of the multiband responses, and the same out-of-band responses for a single sensor are also detected by other multiband sensors with different spectral passbands. The information of multiband radiances recorded by multispectral radiometers distributed at different bands provides a possibility for decomposition. The MDT approach uses the decomposition principle to recover the average narrowband signals from contaminated signals using filter transmittance functions instead of the calibration methods. For an N-channel multispectral sensor, OOB effects are corrected by applying an N×N MDT matrix to the measured signals. The MDT matrixes for SeaWiFS and VIIRS instruments are also reported by Chen and Gao, and Gao and Chen, respectively.
The characteristics of the VIIRS multiband response functions indicate that wavelength intervals of the expected band-averaged (or in-band averaged) spectral radiance are usually less than the partitioned narrow-band intervals in the MDT method. For this reason, there is still some contamination in the recovered narrow-band radiances by the MDT. To address the issue and obtain a highly accurate OOB correction, an Out-of-Band Correction Transform (“OBCT”) method was developed by Chen and Lucke (Chen, W., and R. Lucke, “Out-Of-Band Correction for Multispectral Remote Sensing”, IEEE Trans. Geosci. Rem. Sens., Vol 51, No 3, 10.1109/TGRS.2012.2208975, 2013, incorporated herein by reference). The OBCT method provides a novel approach for dealing with the VIIRS OOB effects and has a significant improvement by comparison to the MDT method.